1. Field of the Invention
The present invention relates to a printing apparatus and a method for detecting a defective jetting nozzle of a printing apparatus.
2. Description of the Related Art
An ink-jet printer using a line head having a print range equal to or more than a width of a printing medium has been known. In this line head, nozzles which jet ink are disposed to face a region extending over the whole width of the printing medium. When printing is performed continuously, paper powder accumulates in a casing of the ink-jet printer. When the paper powder adheres on a nozzle surface of the line head, this nozzle suffers a jetting failure such as defective jetting and jetting amount fluctuation. Consequently, void lines or blurs are formed on the printing medium, resulting in great deterioration in image quality.
It has been known a printing system which performs the jetting failure detection when it is determined, based on the setting by a user, that jetting failure detection should be performed, and if the number P of printed copies after the jetting failure detection performed last time is equal to or more than a predetermined number Pth. In this printing system, the jetting failure detection is performed every predetermined number Pth being a threshold value set in advance by the user. When a defective jetting nozzle is detected, a predetermined recovery operation is performed. Consequently, the defective jetting nozzle is accurately detected and a state in which no defective jetting nozzle exists can be realized.
However, in the above-described conventional printing system, in a case that it is determined, based on the setting by the user, that the jetting failure detection should be performed, the jetting failure detection is always performed every time the number P of printed copies after the jetting failure detection performed last time reaches the predetermined number Pth or more. Therefore, even if no jetting failure is detected in the current jetting failure detection, the next jetting failure detection is performed when the number P of printed copies after the current jetting failure detection reaches the predetermined number Pth or more. Depending on printing paper used, a speed at which the paper powder accumulates in the casing differs. The conventional printing system has a problem of wasteful detection, because the jetting failure detection is performed every time the number of printed copies reaches the predetermined number Pth, even if no jetting failure occurs in the printing during a period up to the predetermined number Pth, unless the setting of the predetermined number Pth is changed by the user.